The present invention relates generally to a power transmission unit for a motor vehicle, and more particularly to a power transmission unit of the type which comprises a trans-axle casing rigidly secured at its upright front seating face to a cylinder block of an engine and having an upper compartment to contain therein a disengageable coupling for connection to a crankshaft of the engine and a lower compartment to contain therein a final drive gearing and a differential gear unit, and a transmission casing sealingly jointed at its upright front seating face to the upright rear seating face of the trans-axle casing to contain therein a change-speed gearing drivingly connected to an output member of the disengageable coupling, and in which the trans-axle casing is provided therein with an upright partition wall to subdivide the lower compartment into front and rear chambers, and the final drive gearing includes a drive pinion shaft supported by a pair of axially spaced bearings carried on the partition wall and having a drive pinion in mesh with a crown wheel to drive the differential gear unit, the drive pinion shaft being coaxially connected to the change-speed gearing.
In such a final drive gearing of the type as described above, the bearing facing to the front chamber is directly splashed with lubrication oil dipped up by rotation of the crown wheel, but the bearing facing to the rear chamber may not be splashed with the dipped up lubrication oil. It is, therefore, necessary to positively lubricate the latter bearing so as to ensure durability of the power transmission unit.